Among the birds of the world, it is usually the males who have the brightest feathers and the females who are the most drab, ...

Not sure whether your leopard gecko is male or female? Thankfully, determining the sex of one of the adorable little lizards ...

Remove the top male spotty fish and, within minutes, the next-in-line female morphs into the tank s new tyrant charging and nipping rivals while her body quietly begins a weeks-long transition to male ...

Background. Most competitive sports segregate male and female athletes due to biologic differences between the sexes. Because exposure to testosterone in males leads to physiologic advantages in ...